1. Field of the Invention
The invention generally relates to a gas turbine, and more particularly, methods and apparatus to repair a rotor disk for a gas turbine.
2. Description of the Related Art
Generally, a compressor rotor wheel assembly of a gas turbine can include a rotor disk and a plurality of rotor blades. The rotor disk can be provided with a plurality of dovetail slots around its periphery and each of the plurality of rotor blades is provided with a dovetail. The dovetail of each of the plurality of rotor blades can be axially inserted in one of the plurality of dovetail slots of the rotor disk to complete the compressor rotor wheel assembly. In some instances, the application of such a compressor rotor wheel assembly is not limited to gas turbines. The compressor rotor wheel assembly can also be used in other power generation and thrust generation applications.
After the rotor disk is installed into the gas turbine, a forward side and an aft side can be defined according to the direction of flow of a working fluid. The working fluid in the gas turbine can enter from the forward side of the rotor disk and escapes from the aft side of the rotor disk. Further, each of the plurality of dovetail slots of the rotor disk can include a pair of dovetail walls and a base of the rotor disk. Each of the plurality of dovetail slots can include a plurality of acute corners located on the base of the rotor disk on the forward and the aft sides of the rotor disk.
During operational conditions, the high rotational speed of the rotor disk and/or thermal gradients can cause the plurality of acute corners to experience high tangential and radial stresses, which may cause an initiation of one or more cracks at the plurality of acute corners of the plurality of dovetail slots. Further, each crack may increase as the rotor disk is in operation.
Conventional methods for repairing a rotor disk for a gas turbine relate to cracks having a length of less than about 0.1 inches (2.5 mm). However, in the case where the length of a crack is greater than about 0.1 inches (2.5 mm), no repair option is defined, and the rotor disk may be scrapped.
Scrapping the rotor disk can directly increase the operational cost of a gas turbine due to the downtime and/or service time needed to disassemble the associated turbine and remove the rotor disk. In light of the above, there is need for a repair methodology of a rotor disk having one or more cracks with the length greater than about 0.1 inches. Furthermore, there exists a need for methods and apparatus to repair a rotor disk for a gas turbine.